This invention relates generally to turbine engines and more particularly, to controlling engine operation.
Known engine control units are configured to operate in multiple control modes for maintaining engine control under many different conditions. The control unit selects a mode of operation based on environmental and operating conditions, and the control unit supplies a fuel flow rate to an engine control processor. The engine control processor then utilizes the fuel flow rate supplied by the control unit to control engine operation.
Known control modes include, for example, a baseline mode, a combustor inlet pressure limiter mode, a fuel acceleration mode, and a fuel deceleration mode. The control unit output for each control mode is fuel flow. The baseline mode corresponds to normal operation of the aircraft engine. The combustor inlet pressure limiter mode is selected when combustor pressures approach maximum permissible limits. The fuel acceleration mode is selected during throttle burst transients to prevent compressor stall and turbine over-temperature. The fuel deceleration mode is selected during throttle chop transients to prevent combustor blowouts. Of course, many other modes are utilized to protect an engine from exceeding operability, mechanical integrity, and other limits, and to provide consistent engine responses.
For each control mode, and to ensure adequate engine control, many factors such as power level, rotor speeds, stall margins, temperatures, and demanded values of thrust are utilized in determining the control unit output. A typical control unit includes numerous single-input, single-output controllers, and each single-input. single-output controller is utilized to generate a value for one commanded actuator position. Specifically, each single-input single-output controller receives a single engine parameter as an input and outputs a value related to fuel flow rate.
The outputs from the controllers are selected based upon the current operation mode of the control unit. Particularly, the control unit output is generated by selecting the outputs from one of the controllers. For example, the controller outputs are selected when meeting a first set of conditions when the control unit is in the baseline mode, and the controller outputs are selected when meeting a second set of conditions when the control unit is in the fuel acceleration mode.
The known control unit described above utilizes simple controllers and selects from among controller outputs to generate the fuel flow rate. It would be desirable to modify the mode selector to improve engine performance. It also would be desirable to be able to set the appropriate control output when using several multivariable controllers.